1. Field of the Invention
The present invention relates to a variable magnification optical system. More particularly, the present invention relates to a variable magnification optical system suitable for, for example, a digital camera or a digital appliance equipped with an image capturing capability that capture an image of a subject with an image sensor, especially a compact zoom lens system that provides a wide angle and a high magnification variation ratio, and to an image-taking apparatus provided therewith.
2. Description of Related Art
In recent years, as personal computers become increasingly widespread, digital cameras which permits easy acquisition of images have been becoming more and more popular. Consequently, there has been a demand for a more compact digital camera and also a demand for an even more compact photographing lens system. Meanwhile, as the number of pixels used in an image sensor tends to increase year by year, there is a demand for an image-taking lens system that can provide a high optical performance to keep up with the increase in the number of pixels used in the image sensor and that is easy to fabricate to keep up with a shortening product cycle. Zooming at a magnification variation ratio as high as over ×7 or ×10 has become a common practice, which brings about an expectation for an even higher magnification variation ratio while an expectation for a wider angle also arises. To satisfy such demands, various types of zoom lens systems have been conventionally proposed (see patent documents 1 to 4, for example).                [Patent document 1] Japanese Patent Application Laid-open No. S63-266414        [Patent document 2] Japanese Patent Application Laid-open No. H8-82743        [Patent document 3] Japanese Patent Application Laid-open No. 2002-98895        [Patent document 4] Japanese Patent Application Laid-open No. 2004-212512        
However, the conventional zoom lens systems proposed suffer from difficulties in simultaneously satisfying such mutually contradictory demands for a higher magnification variation ratio, a more compact size, a higher performance, and for a wider angle. The zoom lens system proposed in patent document 1 has a magnification variation ratio of about ×10, which is hardly considered to be achieving a high magnification variation ratio. The zoom lens system proposed in patent document 2 has a magnification variation ratio as high as ×20, but has a field angle of 70 degrees or less, which is hardly considered to be achieving a wide angle. The zoom lens systems proposed in patent documents 3 and 4 are also hardly considered to be achieving satisfactory balance among a magnification variation ratio, an optical performance, a lens full length, and the like.